The invention generally relates to the field of substrates or structures for producing electronic components, and to methods of producing such structures. It is applicable to semiconductor structures, in particular silicon on insulator (SOI) type structures. The invention also pertains to techniques for assembling layers or substrates on a substrate of a material having atypical surface properties.
FIG. 1 illustrates a conventional structure that includes a silicon layer 4 in which the components are located, and beneath which is a buried oxide layer 2. A silicon substrate 6 acts as a mechanical support. The oxide layer 2 provides insulation from stray currents and charges from ionized particles. It also provides good insulation between neighboring components formed in the same silicon layer, and in particular the oxide layer substantially reduces stray capacitance between the neighboring components.
The superficial silicon layer 4 is typically about 10 nanometers (nm) to 1000 nm thick, while the oxide layer 2 is on the order of several hundred nanometers thick, for example 400 nm. This type of structure can be obtained by using a “SIMOX” type process or by using a “wafer bonding” technique that relies on molecular bonding.
After producing an assembly such as that shown in FIG. 1, electronic components can be fabricated in the superficial silicon layer 4. The silicon layer 4 is therefore an active layer; the oxide layer 2 is an insulation layer; and the substrate 6 acts as a mechanical support that allows for processing of the assembly.
Proper operation of a component fabricated in the layer 4 depends upon various parameters. One of the parameters is heating, which can substantially limit the performance of the component. Thus, it would be advantageous to have a semiconductor on insulator type structure, and a method of producing such a structure, in which heating does not limit the performance of the subsequently produced components, or minimally limits the performance in comparison to known structures.
Furthermore, known techniques for assembling materials do not allow bonding of substrates or layers having an atypical surface that has a roughness of more than a certain limiting value on the order of 0.5 nm root mean square (rms), or which are difficult to polish, or which have a chemical composition that is not conducive to molecular bonding. Occasionally a need arises to bond materials that have a roughness above the limiting value, or wherein at least one of the materials is difficult to polish or has a chemical composition that is not conducive to bonding by molecular bonding, or to bond such a material with a layer or substrate of a material that may itself be compatible with direct bonding or molecular bonding.